The discussion in this section is not limited to discussion of work that qualifies as "prior art" against the present invention. Therefore, no such admission and no declaration against the present inventors' interests shall be implied by reason of this discussion.
Multiple Sclerosis (MS) is a chronic inflammatory disease of the white matter of the human central nervous system and is believed to be of autoimmune etiology. Regardless of its etiology, MS is accompanied by autoimmune attack of nerve tissue. For example, the disease is characterized by prominent T-cell and macrophage infiltrates into nervous tissue (i.e., the brain, spinal cord, peripheral nerves or associated cell types), demyelination and neurological dysfunction. Myelin basic protein (MBP) has been extensively studied by the present inventors, their co-workers and others as an autoantigen in the disease because of its role as an inducing agent in the major animal model of MS, experimental allergic encephalomyelitis (EAE), as well as its role in the human disease post-viral encephalomyelitis. In addition, the present inventors and their co-workers have studied MBP as a "bystander antigen" (Ser. No. 843,752, supra).
A major hypothesis regarding the pathogenesis of MS is that T-cells reactive with myelin basic protein in the white matter of the CNS initiate the inflammatory process. Another hypothesis is that T-cells reactive with proteolipid protein (PLP) initiate the inflammatory process. The demonstration that activated T-cells specific for myelin basic protein (MBP) can be isolated from MS patients (Allegretta, M., et al., Science: 247: 778, 1990) further implicates MBP-reactive T-cells in the pathogenesis of the disease. The work of the present inventors also shows that MBP-reactive T-cells are involved in the pathology of the disease, subsequent to initiation of the inflammatory process. (As will be described in more detail below, the present inventors demonstrated that healthy individuals also often have MBP-specific T-cells, but unlike those of MS patients, MBP-specific T-cells from healthy individuals are not activated.)
The current treatments for MS are solely palliative and involve administration of drugs which act in a non-specific fashion to suppress the immune response in the subject. Examples of such drugs are cyclophosphamide, Imuran (azathioprine) and Cyclosporin A. Steroid compounds such as prednisone and methyl-prednisolone are also employed in many instances. These drugs have limited efficacy against MS. Use of such drugs is limited by their toxicity and by the fact that they induce "global" immunosuppression upon. prolonged use, i.e., they also down-regulate the normal protective immune response to pathogenic microorganisms thereby increasing the risk of infection. In addition, patients that are globally immunosuppressed for prolonged periods of time run an increased risk of developing certain malignancies.
More details on the immunological processes occurring are known for experimental allergic encephalomyelitis (EAE), the primary animal model for MS. EAE can readily be induced in small mammals by immunization with myelin basic protein (MBP) in an appropriate adjuvant or by adoptive transfer through the injection of CD4.sup.+, MBP-reactive T-cells (Alvord Jr, E. C., et al. eds. in Experimental Allergic Encephalomyelitis: A Useful Model for Multiple Sclerosis, A. R. Liss, N.Y., 1984; Makhtarian, D. E., et al. Nature 305:356, 1984; Ben-Nun, A. et al. J. Immunol. 129:303, 1982). The T-cells that induce EAE in both mice and rats, termed encephalitogenic cells, specifically recognize peptides corresponding to the immunodominant regions of MBP. The presentation of these regions to the T-cells occurs on the surface of antigen-presenting cells (APCs) in association with unique Major Histocompatibility Complex. (MHC) class II molecules. It should be emphasized that immunodominant regions of MBP, that is the portion of the protein most often recognized by MBP-reactive T-cells of the CD4.sup.+ type, differs depending on the species of the host mammal and may also differ depending on the species of MBP, despite the fact that the amino acid sequence of MBP exhibits very high interspecies homology. For example, as the present inventors and their co-workers have discovered, an immunodominant epitope of human MBP in humans is contained within the subsequence of the human MBP molecule comprising amino acids 84-102. Another immunodominant epitope can be found in the subsequence of the human MS molecule comprising amino acids 143-168. This is evidenced by the specificity of human T-cells isolated from individuals afflicted with MS (related patent application Ser. No. 502,559 and Example 1 below). The immunodominant region of mouse MBP is amino acids 1-9 when administered to mice (Zamvil et al., Nature 324:258, 1986) and that of rat MBP is amino acids 68-88 when administered to rats (Burns et al., J. Exp. Med. 169:27, 1989). On the other hand, the immunodominant region of guinea-pig MBP in rats is located within residues 75-84 (Hashim, G. Myelin: Chemistry and Biology, Alan R. Liss, N.Y. 1980).
Based on the work done in the EAE system, alternative therapies are being developed for the treatment of autoimmune diseases in general and MS in particular. U.S. patent application Ser. No. 65,794 filed Jun. 24, 1987 (now abandoned) and co-pending International Patent Application PCT/US88/02139, filed Jun. 24, 1988, now in national stage as United States application Ser. No. 07/460,852 and a continuation-in-part of this application, United States application Ser. No. 07/596,936, disclose that oral or enteral administration of whole myelin basic protein as well as disease-inducing and non-inducing fragments and analogs thereof is effective in suppressing acute monophasic EAE and are useful in suppressing MS symptoms when similarly administered.
The following co-pending commonly assigned patent applications are also of interest: U.S patent application Ser. No. 454,806 filed Dec. 20, 1989 discloses the aerosol administration of autoantigens, disease-suppressive fragments of said autoantigens and analogs thereof as an effective treatment for treating T-cell mediated autoimmune diseases such as MS.
U.S. application Ser. No. 07/487,732, filed Mar. 20, 1990 entitled "Enhancement of the Down Regulation of Autoimmune Diseases by Oral Administration of Autoantigens" discloses synergists (enhancers) for use with oral administration of autoantigens, disease-suppressive fragments and analogs thereof as effective treatments for T-cell mediated autoimmune diseases.
U.S. application Ser. No. 07/843,752 discloses methods and compositions for treating autoimmune diseases orally or by inhalation by administering bystander antigens. Bystander antigens are tissue-specific antigens that are present at the locus of autoimmune attack and that have the ability upon their being orally administered to generate T-suppressor cells which in turn suppress immune attack at the afflicted tissue. Bystander antigens are not necessarily autoantigens and are not necessarily themselves the target of immune attack. (In fact, there is evidence that the immunosuppressive epitope(s) of an autoantigen are different from the immunodominant epitope(s) thereof, although immunodominant epitopes (which do elicit suppression upon oral administration) may act as bystander antigens in suppressing immune attack directed against other portions of the same antigen or portions of other antigens in the afflicted tissue.) However, bystander antigens must (a) be specific to the afflicted tissue and (b) possess the ability to elicit T-suppressor cells upon oral administration.
It has now been found that oral administration of multiple doses and small amounts of whole antigens containing encephalitogenic immunodominant epitopes elicits this type of active suppression. On the other hand, i.v. administration of entire autoantigen (or of one or more encephalitogenic immunodominant epitope-containing fragments thereof) also induces suppression but only of immune attack T-cells recognizing epitopes of the autoantigen. The latter type of suppression, which is believed to proceed via the mechanism of clonal anergy, is also observed upon oral administration of single doses and large amounts of antigens encompassing encephalitogenic epitopes, specifically immunodominant epitopes, especially when such antigens are accompanied by protease inhibitors.
For human MBP, a protein believed to be an autoantigen for MS, extensive testing by the present inventors has revealed fragments of the protein incorporating epitopes which are recognized by a large number of MBP-specific immune attack (CD4.sup.+) T-cells isolated from MS patients. Such fragments, comprising immunodominant epitopes, are likely candidates for administration to patients suffering from MS, with the goal of suppressing autoimmune response, and particularly suppressing the function of MBP-reactive T-cells that are responsible for autoimmune attack on nervous tissue. To that end, the present invention contemplates not only oral administration of such peptide fragments to mammals in need for such treatment but also parenteral administration of such fragments.
Therefore, it is an object of the present invention to provide immune-suppressive agents, specifically fragments of human MBP, and methods of using these fragments to suppress human T-cell functions.
Another object of the present invention is to provide compositions and pharmaceutical formulations comprising these fragments of human MBP useful for oral and/or i.v. administration to humans, and methods of use of such formulations.
Yet another object of this invention is to provide, as a reagent that could be used to determine the specificity of human T-cells, a peptide fragment of MBP incorporating an immunodominant epitope.
A further object is to provide compounds and compositions that anergize MBP-reactive T-cells or cause active suppression of such T-cells, the latter being evidenced for example by suppression of proliferation of MBP-reactive T-cells.
These and other objects of the present invention will be apparent to those of ordinary skill in the art in light of the present specification, drawings and claims.